Spunbonded nonwoven fabrics formed of nylon 6,6 are widely used commercially for a number of purposes. Such fabrics exhibit excellent strength and permeability properties and accordingly are desirable for use in construction fabrics, filtration material, and furniture and bedding backing materials.
The fabrics are produced via the well-known spunbonding process in which molten nylon 6,6 is extruded into filaments, and the filaments are attenuated and drawn pneumatically and deposited onto a collection surface to form a web. The filaments are bonded together to produce a strong coherent fabric. Filament bonding is typically accomplished either thermally or chemically, i.e., autogenously. Thermal bonding is accomplished by passing the web of filaments between the nip of a pair of cooperating heated calender rolls. In autogenous bonding, the web of filaments is transported to a chemical bonding station or "gas house" which exposes the filaments to an activating agent (i.e., HCl) and water vapor. Water vapor enhances the penetration of the HCl into the filaments as they have a high moisture affinity. The HCl causes the filaments to become tacky and thus amenable to bonding. Upon leaving the bonding station, the web passes between rolls which compact and bond the web. Adequate bonding is necessary to minimize fabric fuzzing (i.e., the presence of unbonded filaments) and to impart good strength properties to the fabric. Autogenous bonding has been especially used in forming spunbonded nylon 6,6 industrial fabrics.
In autogenous bonding, the effectiveness of the bonding operation can be adversely affected by certain process variations, resulting in variations in such properties as abrasion resistance (fuzzing) or fabric strength. For example, slight changes in HCl and water vapor content will have a significant affect on the degree of filament bonding. U.S. Pat. No. 3,853,659 to Rhodes addresses this problem and provides a process for autogenously bonding continuous nylon filaments in which water vapor and HCl amounts were optimized to improve fabric bonding. In spite of these efforts, Rhodes suggests that control of these variables can be difficult. For example, if the moisture level is too high and condensate deposits on the fiber surface, the fibers will disintegrate, since HCl is a known solvent for nylon. On the other hand, at certain low humidity levels, water evaporation from the fibers will cause them to loose their surface tackiness and not adhere adequately to one another. As a result, the fabric will display poor abrasion resistance and poor strength properties.
A number of uncontrolled factors also sometimes adversely affect the formation and attenuation of the nylon filaments for the spunbond fabric. For example, variations in polymer properties, such as crystallinity, can adversely affect extrusion and attenuation, resulting in filament breakage, poor filament deposition, hanging of filaments in the attenuator, plugging of the attenuator, and other problems. These difficulties can cause substantial loss in fabric yield along with nonuniformities in the fabric. These problems can sometimes be alleviated by altering the temperature at which the fibers are melt spun. However, one severe drawback of this solution is that it often takes several hours for the extruder and piping to reach its new temperature and to become stabilized at the new spinning conditions. During this time, large quantities of unacceptable fabric may be produced.